1. Field of the Invention
The present invention relates to a rotation connector adapted to the transmission of electrical signals from a first device to a second device, which second device is rotatable with respect to the first device. The rotation connector includes a substantially dielectric support member having a longitudinal direction and provided with a first end portion and a second end, wherein the support member comprises an electrically conductive track extending in the longitudinal direction as far as the region of the second end portion, a self-supporting contact ring having a substantially circular electrically conductive peripheral edge and an inner edge defining a recess around the center-line of the contact ring, said contact ring being fixed on the support member. The recess substantially encloses the support member in such a manner that the center-line of the contact ring is substantially parallel to the longitudinal direction of the support member. The peripheral edge of the contact ring is connected to the track via an electrically conductive path. The present invention also relates to a contact ring, an insulator element, and a support member for use in such a rotation connector. In addition, the invention relates to a method of making the rotation connector.
2. Related Art
A connector of this kind, which is also known as a slip ring, is known from the prior art. FIG. 1 is a diagram of a rotation connector of this kind. This connector is made as follows: In a first step, an electrically conductive wire provided with an insulating coating is soldered or spot-welded to the inner edge of a (frequently) brass contact ring. As many contact rings as are necessary for the type of connector can be made in this way. A first contact ring is then placed in a jig. A second contact ring is then pushed over the wire fixed to the first contact ring and the second contact ring is placed close to the first contact ring so that they do not make contact with one another. A third contact ring is then pushed over the two wires of the first and second contact rings, and this third ring is pushed close to the second contact ring, again without making contact. A row of contact rings is built up in this way. The row is then embedded, possibly via an injection moulding process, in a dielectric plastic which after cooling and/or chemical hardening forms a rigid support member for the contact rings. As a result, the contact rings are permanently fixed and insulated from one another in the connector. In addition, the wires which serve as electrically conductive tracks from the respective contact rings to the second end of the rotation connector, are rigidly fixed in the plastic on the inside of the support member. The next step is to turn the injection moulding in a lathe so that the conductive cylindrical surface of the contact rings is exposed. Finally the connector is provided on the outside of the contact rings with a brush which includes a plurality of individual brush elements as there are contact rings in the connector. The brush provides the electrical contact between the contact rings and the surroundings of the connector. In this way conductive connections can be made between the brush and the wires which emerge at the second end of the rotation connector.
The connector is used by connecting the brush to a first device and by connecting the wires emerging from the connector near the second end portion to a second device which can rotate with respect to the first device. With this construction of the connector, the electrical contact between the two devices is maintained even when the second device rotates with respect to the first device.
The known rotation connector, however, has a number of significant disadvantages. Above all, the assembly of this known connector involves a very labor-intensive process. Thus placing the contact rings over the wires of the preceding rings cannot be automated, so that this operation requires considerable expensive working time. In addition, during the moulding of the plastic support member, there is a considerable risk that one or more of the wires on the inside of the contact rings will work loose, because the soldered or spot-welded connection is mechanically weak. Also, after the moulding of the plastic support member, each connector must be individually finished on a lathe. Not only is this also a labor-intensive operation, but it also increases the risk of defects, for example a complete breakage of the connector or breakage of the emerging wires, in the connector which has already been largely assembled. Such defects, e.g., the working loose of a soldered connection as described above, cannot be remedied after the support member has been moulded. This means that the production costs due to rejects of practically completely assembled connectors become even more expensive. Another significant disadvantage is that the wires extend substantially through the center of the support member. In this way it is difficult, particularly in the case of small connectors, to combine the same with other forms of signal transmission for which space is required in the connector. Thus, in modern communications technology, signal transmission is frequently effected by optical fibers, which can hardly be accommodated, if at all, in the support member, because there is practically no room for them, while on the other hand the support member is not sufficiently transparent for direct transmission of optical signals, due to the presence of the wires. Even for other more conventional signal transmission, such as capacitative and inductive transmission, the known connector is unsuitable because components would have to be accommodated in the core of the support member for this purpose. Although that is not completely impossible, it would result in connectors which are difficult to miniaturize, if they can be miniaturized at all.
The object of the present invention is to provide a rotation connector which is simple to assemble and which is adapted to being combined with a second form of signal transmission. To this end, a rotation connector according to the preamble of claim 1 has been developed, wherein the track is disposed on the surface of the support member. The connector according to the present invention is made by providing the surface of the support member with at least one conductive tracks, for example in the form of a thin metal layer. The contact ring is then pushed over the support member in such manner that it makes electrically conductive contact with the track. A second contact ring can then be pushed over the support member in the direction of the first, and this contact ring makes contact with a second track. In this way, the connector can be constructed very simply and by automatically. Any defects, for example a non-functioning contact ring, can easily be remedied by removing such contact ring from the connector and replacing it by another. A defect in a track, for example a break, where no electrically conductive through the connection is achieved, can also easily be remedied by removing the contact ring or rings from the connector and repairing the track. Also, the construction of the connector according to the present invention enables the support member to be made hollow so that other components can be accommodated in the cavity, for example, a means for the optical transmission of data from the first device to the second device.
In one embodiment, the track is formed as a first profile in the surface of the support member and, the inner edge of the contact ring is provided with a second profile which is in operative connection with the first profile. This embodiment offers the advantage that the assembly of the connector is further simplified because it is then possible to form the contact ring in such a manner that it can be pushed on the support member in only one way with the conductive contact being, at all times, formed via the co-operating profiles. It also offers the possibility of arranging that any following contact ring will always be in electrically conductive connection with a subsequent track by ensuring that each subsequent contact ring is pushed with its profile over a following track.
In one preferred embodiment, the first profile is a recess in the said surface and the second profile is a projection on the inner edge of the contact ring. This embodiment has the advantage that the various parts, and particularly the support member, can be made in very simple manner, for example by injection mouldings. The support member, which is made substantially from an electrically insulating material, e.g. a dielectric plastic, can also be provided with channels in the longitudinal direction by a machining operation, for example milling. By finishing on a lathe a substantially circular peripheral edge can thus be formed in a simple manner.
In one embodiment, the contact ring is connected to the said track under pressure at the electrical transition between the contact ring and the track. This embodiment, in which the projection on the inner edge of the contact ring is held under pressure against the corresponding track, formed as a channel, offers the advantage that the electrical transition between the contact ring and the track is reliable. In addition, good mechanical anchoring of the contact ring on the support member is obtained in this way so that the connector is operationally more reliable.
In a preferred embodiment, the contact ring is so shaped that the projection on the inner edge is resiliently displaceable with respect to the contact ring. For example, by providing a recess in the contact ring close to the location where the projection is situated, on the inner edge, it is possible, without using additional means, for the projection to spring with respect to the contact ring. This can be utilised in order to place the projection under pressure in the track formed as a channel. An additional advantage is that the mechanical anchoring of the contact ring on the support member is further improved.
In one embodiment, the contact ring is removably fixed on the support member. This embodiment has the advantage that the rotation connector can, at all times, be repaired and a more flexible system is also obtained.
In another embodiment, the contact ring is a plastic product provided with a conductive coating, said coating comprising at least a part of the conductive path. This embodiment offers a number of significant advantages. Firstly, a contact ring according to this embodiment can be produced very simply, for example by injection moulding of a suitable plastic in a jig and then providing the ring with a conductive coating. This can be effected in a manner sufficiently known from the prior art to one skilled in the art, for example, by vapor coating of a metallic layer, or by application of a conductive plastic from a solution, or electroplating a metallic layer in a bath suitable for the purpose, etc. A contact ring of this kind can easily be obtained in any desired shape. On the one hand the conductive coating ensures a conductive peripheral edge while on the other hand it forms part of the conductive path from said peripheral edge to the projection on the inner edge. The result is a reliable electrical connection between the peripheral edge and the conductive track on the support member.
In one embodiment, the peripheral edge is provided with a substantially continuous groove in the tangential direction. A groove of this kind is used to accommodate the conductive element of a brush, for example a wire, or a bunch of wires (in the tangential direction). As a result this wire will not lose contact with the peripheral edge because the walls of the groove hold the wire in the middle of the contact ring. Also, the contact surface with the wire of the brush and the peripheral edge is larger than if the peripheral edge is constructed as a flat edge. In one preferred embodiment, wherein the connector also comprises an electrically conductive brush which is in contact with the peripheral edge of the contact ring, the groove is in communication with two brushes. By connecting the groove with two brushes, an operationally more reliable connector is obtained because the risk of two brushes breaking down simultaneously is many times reduced. Although provision of a second brush means that the production costs for the connector are increased, such increase is minimal. In addition, this is compensated as far as the connector user is concerned by a more reliable connector, which consequently has to be replaced or repaired much less frequently.
The advantages of the present invention can be utilised particularly if the rotation connector is provided with at least two conductive mutually insulated tracks, and the rotation connector also comprises at least two contact rings corresponding to these tracks, each contact ring being in electrically conductive connection with one track and the contact rings being fixed on the support members so as to be insulated from one another. The production of a connector of this kind, in particular, will require much less time and particularly less labor, than the known connector. In one preferred embodiment, the contact rings are of substantially the same shape. This means a further simplification of the product and hence a further reduction of the costs.
In another embodiment, the rotation connector is also provided with insulator elements disposed between the two contact rings. By means of a ring of this kind, it is a simple matter to fix two contact rings on the support member so that they are insulated from one another. These insulator elements also, for example constructed as substantially annular self-supporting elements having a recess corresponding to that of the contact rings, can also be made in the same shape so that the number of different elements from which the connector is constructed is limited.
In a further preferred embodiment, the insulator element is provided with a third profile in co-operating connection with the first profile in the form of tracks. An insulator element of this kind, the inner edge of which is thus provided with, for example, projections which are substantially of the same shape as the cross-section of each of the tracks, can thus be easily mechanically fixed on the support member. By making a co-operating connection between the insulator element and at least one contact ring, there is good mutual fixing of the contact ring and the insulator element. This has the great advantage that the function of the mechanical fixing of the contact rings and insulator elements on the support member can be practically completely stopped in the form of the insulator elements. In this way, the functions for fixing and electrical conduction can be further separated, thus making the product more tolerant, because each of the components has to combine less functions in itself.
In one embodiment, the region of the first end of the rotation connector is provided with a flange to support the set of contact rings and insulator elements on the support member, and the second end is adapted to provide a plug comprising at least two connecting elements for the electrical connection of the tracks to the said second device. The said flange makes the production of the rotation connector even simpler, because the first contact ring or the first insulator element can simply be pushed against the flange so that said first element is fixed at a distinct location. Subsequent contact rings and insulator elements will then arrive at a distinct location as if of themselves. In this preferred embodiment, the second end is provided with the facility for fitting a plug for connecting the second device, said plug normally having as many connecting or contact elements as there are tracks on the support member, each connecting element corresponding to a track. It is also possible to construct a connecting element that makes contact with two or more tracks simultaneously. This embodiment is advantageous if heavier currents are required. In this way, the current flowing through a number of tracks can be collected and this has the advantage that each of the tracks does not of itself have to be made more rugged.
In a further preferred embodiment, the connecting elements are in contact with the corresponding tracks under pressure. This improves the electrical transition from the track to the plug. A pressure of this kind can be created, for example, by making the connecting elements in the form of thick wires which are convex in the region of the track in the direction of the latter, so that they can form a good point contact under pressure.
In one preferred embodiment, the rotation connector is provided with a continuous cavity from the first end portion to the second end portion, the cavity being provided with a means for transmitting signals. The rotation connector according to the present invention enables the transmission of electrical signals via the connector itself to be easily combined with the transmission of subsequent signals. This combination has the important advantage that there is no need for a plurality of communication lines between the first and second device and yet the transport of all kinds of signals can be combined in one connector. This means a considerable saving of costs and gives greater freedom for the design of systems in which a combination of this kind is necessary. A connector combined in this way can be used, for example, for high grade applications where it is necessary to provide a rotatable device with electrical signals and other signals, particularly data. Such applications are found in particular in information and communication technology, for example in surveillance cameras, digital printers, aircraft, guided missiles, and so on.
In one particular embodiment, the said means for transmitting signals is a transparent medium for transporting optical signals. A medium of this kind enables data to be transported through the connector at very high speed. Examples of printers in which a rotation connector according to the present invention, and particularly according to the embodiment combined with a high speed data link, can be used are described in U.S. Pat. Nos. 4,704,621 and 5,742,320 and European Patent Application EP 0 991 259.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.